The present invention relates to an intermediate support structure for holding a row of long moving blades in a steam turbine. More particularly, the invention relates to an intermediate support structure for holding rows of long moving blades in low-pressure stage of a steam turbine, and relates to a steam turbine.
In a typical steam turbine, the moving blade rows are arranged peripherally and planted on the outer circumferential surface of the turbine rotor. The stationary blade rows are secured to the turbine casing. The moving blade rows and the stationary blade rows are alternately arranged in the axial direction of the turbine rotor. One moving blade row and one stationary blade row (called “nozzles”) make a blade row pair, which is known as “a stage.” The stages are axially arranged, constituting the turbine. As fluid flows through the gap between the blades of every stage, the turbine rotor rotates.
Thus, the moving blades of the steam turbine convert the energy of steam to a mechanical rotational force, which is transmitted to the turbine rotor. Steam at high temperature and high pressure gradually expands, flowing through the stages, each composed of moving blades and nozzles, and exerting a rotational force to each moving blade.
The moving blades are planted on the turbine rotor, and the turbine rotor rotates at high speed. A large centrifugal force and rotational vibration are inevitably applied, particularly, to the long moving blades that are used in the low-pressure stages of the steam turbine. In addition, the rows of long moving blades are important components because they significantly affect the efficiency of the entire turbine, the output power of the turbine and the size of the plant including the turbine. Hence, it is important to make sure that the rows of long moving blades have an appropriate strength in the process of designing the steam turbine.
To reinforce the rows of long moving blades, making them strong enough to withstand the above-mentioned large centrifugal force and rotational vibration, intermediate support members, such as tie wires or lugs, have hitherto been used, coupling the moving blades to one another in peripheral direction. The moving blade rows are thereby reinforced (see Japanese Patent Application Laid-Open Publication Nos. 06-248902 and 06-010613, the entire contents of which are incorporated herein by reference.).
As shown in FIGS. 1 and 2, the conventional intermediate support members that reinforce the strength of the moving blade rows are lugs 3 (FIG. 2), or lugs and sleeves, or tie wires (not shown). The intermediate support members have a circular or elliptical cross section. So shaped, the intermediate support members greatly block the main steam flow that passes through the gap between any two adjacent moving blades 1. Consequently, the main-steam flow separation is induced as shown in FIGS. 3 and 4, inevitably causing the fluid loss.